Low Energy Ion Research Articles

Morphology of Buried Interfaces in Ion-Assisted Magnetron Sputter-Deposited 11B4C-Containing Ni/Ti Multilayer Neutron Optics Investigated by Grazing-Incidence Small-Angle Scattering.

Multilayer neutron optics require precise control of interface morphology for optimal performance. In this work, we investigate the effects of different growth conditions on the interface morphology of Ni/Ti-based multilayers, with a focus on incorporating low-neutron-absorbing 11B4C and using different ion assistance schemes. Grazing-incidence small-angle X-ray scattering was used to probe the structural and morphological details of buried interfaces, revealing that the layers become more strongly correlated and the interfaces form mounds with increasing amounts of 11B4C. Applying high flux ion assistance during growth can reduce mound formation but lead to interface mixing, while a high flux modulated ion assistance scheme with an initial buffer layer grown at low ion energy and the top layer at higher ion energy prevents intermixing. The optimal condition was found to be adding 26.0 atom % 11B4C combined with high flux modulated ion assistance. A multilayer with a period of 48.2 Å and 100 periods was grown under these conditions, and coupled fitting to neutron and X-ray reflectivity data revealed an average interface width of only 2.7 Å, a significant improvement over the current state-of-the-art commercial Ni/Ti multilayers. Overall, our study demonstrates that the addition of 11B4C and the use of high flux modulated ion assistance during growth can significantly improve the interface morphology of Ni/Ti multilayers, leading to improved neutron optics performance.

Plasma enhanced atomic layer deposition of silicon nitride using magnetized very high frequency plasma

To obtain high-quality SiN x films applicable to an extensive range of processes, such as gate spacers in fin field-effect transistors (FinFETs), the self-aligned quadruple patterning process, etc, a study of plasma with higher plasma density and lower plasma damage is crucial in addition to study on novel precursors for SiN x plasma-enhanced atomic layer deposition (PEALD) processes. In this study, a novel magnetized PEALD process was developed for depositing high-quality SiN x films using di(isopropylamino)silane (DIPAS) and magnetized N2 plasma at a low substrate temperature of 200 °C. The properties of the deposited SiN x films were analyzed and compared with those obtained by the PEALD process using a non-magnetized N2 plasma source under the same conditions. The PEALD SiN x film, produced using an external magnetic field (ranging from 0 to 100 G) during the plasma exposure step, exhibited a higher growth rate (∼1 Å/cycle) due to the increased plasma density. Additionally, it showed lower surface roughness, higher film density, and enhanced wet etch resistance compared to films deposited using the PEALD process with non-magnetized plasmas. This improvement can be attributed to the higher ion flux and lower ion energy of the magnetized plasma. The electrical characteristics, such as interface trap density and breakdown voltage, were also enhanced when the magnetized plasma was used for the PEALD process. Furthermore, when SiN x films were deposited on high-aspect-ratio (30:1) trench patterns using the magnetized PEALD process, an improved step coverage of over 98% was achieved, in contrast to the conformality of SiN x deposited using non-magnetized plasma. This enhancement is possibly a result of deeper radical penetration enabled by the magnetized plasma.

Sputtering of silver nanoparticles bombarded with 3–100 keV Ar ions

Rutherford backscattering spectrometry and scanning electron microscopy were applied to obtain sputtering yields of Ag nanoparticles (5–30 nm in diameter) under 3–100 keV Ar+ ion irradiation. For low-energy ion irradiation, the diameter dependence of the sputtering yield was approximately 1.5 times higher than that of the bulk at diameters of a few nanometers, and then approached the bulk value at larger diameters. Under high-energy ion irradiation, especially for 100 keV Ar+ irradiation, the sputtering yields of Ag nanoparticles with diameters as small as a few nanometers were extremely higher than those predicted by the theoretical calculations. We concluded that such high sputtering yield originated in Ag cluster emission.

Molybdenum assisted self-organized pattern formation by low energy ion beam sputtering

Molybdenum assisted self-organized pattern formation by low energy ion beam sputtering

Unveiling the nature of atomic defects in graphene on a metal surface.

Low-energy argon ion bombardment of graphene on Ir(111) induces atomic-scale defects at the surface. Using a scanning tunneling microscope, the two smallest defects appear as a depression without discernible interior structure suggesting the presence of vacancy sites in the graphene lattice. With an atomic force microscope, however, only one kind can be identified as a vacancy defect with four missing carbon atoms, while the other kind reveals an intact graphene sheet. Spatially resolved spectroscopy of the differential conductance and the measurement of total-force variations as a function of the lateral and vertical probe-defect distance corroborate the different character of the defects. The tendency of the vacancy defect to form a chemical bond with the microscope probe is reflected by the strongest attraction at the vacancy center as well as by hysteresis effects in force traces recorded for tip approach to and retraction from the Pauli repulsion range of vertical distances.

Complex dayside particle precipitation observed during the passage of a solar wind rotational discontinuity

The dayside particle precipitation during the passage of a solar wind rotational discontinuity (RD) event on 10 April 2015 is examined and reviewed. The RD leads to complex structures at the magnetopause, boundary layer, mantle, and cusp even though the geomagnetic activity level remains low. Particle precipitation data from DMSP F17 reveal the formation of an unusual boundary layer where the low energy (cold) ions exhibit energy-latitude dispersion that is usually associated with mantle while the high energy (hot) ions look like typical magnetospheric ions. DMSP F17 and F19 observe a double cusp that is a signature of magnetic reconnection occurring at both high- and low-latitudes due to the dominant IMF By. A global MHD simulation of the event supports the existence of the simultaneous reconnections at high- and low-latitude magnetopause that are consistent with the anti-parallel and component merging models, respectively. Finally, Cluster C2, located at high-latitude and high-altitude in the southern hemisphere, observes velocity fluctuations and reversals with peak-to-peak amplitudes >800 km·s–1 as it crosses the magnetopause. Guided by the MHD simulation, the Cluster observation can be interpreted as the spacecraft crossing reconnection outflows while moving from one side of the X-line to the other.

Modification of Cu Oxide and Cu Nitride Films by Energetic Ion Impact

We have investigated lattice disordering of cupper oxide (Cu2O) and copper nitride (Cu3N) films induced by high- and low-energy ion impact, knowing that the effects of electronic excitation and elastic collision play roles by these ions, respectively. For high-energy ion impact, degradation of X-ray diffraction (XRD) intensity per ion fluence or lattice disordering cross-section (YXD) fits to the power-law: YXD = (BXDSe)NXD, with Se and BXD being the electronic stopping power and a constant. For Cu2O and Cu3N, NXD is obtained to be 2.42 and 1.75, and BXD is 0.223 and 0.54 (kev/nm)−1. It appears that for low-energy ion impact, YXD is nearly proportional to the nuclear stopping power (Sn). The efficiency of energy deposition, YXD/Se, as well as Ysp/Se, is compared with YXD/Sn, as well as Ysp/Sn. The efficiency ratio RXD = (YXD/Se)/(YXD/Sn) is evaluated to be ~0.1 and ~0.2 at Se = 15 keV/nm for Cu2O and Cu3N, meaning that the efficiency of electronic energy deposition is smaller than that of nuclear energy deposition. Rsp = (Ysp/Se)/(Ysp/Sn) is evaluated to be 0.46 for Cu2O and 0.7 for Cu3N at Se = 15 keV/nm.

Superalkalis with Hydrogen as Central Electronegative Atom and their Possible Applications: Ab Initio and DFT Study.

Superalkalis are unusual species having ionization energies lower than that of the alkali metals. These species with various applications are of great importance in chemistry due to their low ionization energies and strong reducing property. A typical superalkali contains a central electronegative core decorated with excess metal ligands. In the quest for novel superalkalis, we have designed the superalkalis HLi2, HLiNa and HNa2 using hydrogen as central electronegative atom for the first time employing high level ab initio (CCSD(T), MP2) and density functional theory (ωB97X-D) methods. The superalkalis exhibit very low ionization energies, even lower than that of cesium. Stability of these species is verified from binding energy and dissociation energy values. The superalkalis are capable of reducing SO2, NO, CO2, CO and N2 molecules by forming stable ionic complexes and therefore can be used as catalysts for the reduction or activation of systems possessing very low electron affinities. The superalkalis form stable supersalts with tailored properties when interact with a superhalogen. They also show remarkably high non-linear optical responses, hence could have industrial applications. It is hoped that this work will enrich the superalkali family and spur further theoretical and experimental research in this direction.

Electrostatic lens design applied to low energy ion beam calibration system

Low energy ion detection in space is one of the most important interests of space exploration. An accurate calibration of this type of instrument is necessary to ensure the effectiveness and scientificness of the obtained data. And the ion beam system is the most critical equipment in a calibration facility. In this study, an initial ion beam is generated by a Kaufman ion source and a set of electrostatic lenses is designed to expand and attenuate the ion beam. The simulation results indicate that the beam density of the ion beam can be attenuated by more than three orders of magnitude. This design reduces the space requirements and usage costs of the entire calibration system, and provides a guidance for the design of a calibration systems at the energy range of 100–1000 eV.

Prolonged pattern coarsening in ion irradiated swinging Si substrates

Low energy ion beams are regarded as an effective means to spatio-temporally pattern a wide variety of surfaces that exhibit intriguing motifs. In this work, an unconventional technique of surface patterning has been demonstrated by studying the topographical evolution of a Si(100) surface in the presence of azimuthal sample swinging (Δϕ=20∘) under 500 eV Ar+irradiation with a polar incidence angle of 67°. A prolonged wavelength coarsening is also noticed for the swinging sample. Ripple anticoarsening is observed for static sample at high fluences. The linear and nonlinear growth regimes are found to bear a direct consequence of this unconventional geometry. Furthermore, two-dimensional slope distributions of the surface morphologies clearly indicate reduced asymmetries in the surface structures. The present geometry brings in an additional factor of differential exposure and redeposition effects in addition to the near-surface mass redistribution, the former being inconceivable in the static configuration. This study establishes the role of this unconventional yet simple method to precisely modify and control surface asymmetries and influence regime shifts.

Uniformity of low-pressure capacitively coupled plasmas: Experiments and two-dimensional particle-in-cell simulations

Radio-frequency capacitively coupled plasmas (CCPs) are one of the key technologies enabling the latest etching processes in 3D NAND and FinFET manufacturing. These processes rely crucially on the precise control of the uniformity of ion/radical fluxes and ion angular and energy distribution function (IAEDF) in CCPs. The plasma behavior and scaling properties are dependent on the plasma chemistry in these processes, e.g., electro-positive Ar plasmas vs highly electro-negative O2 plasmas. With the large number of process and design parameters influencing the plasma properties, computational modeling has become an important tool in conjunction with experimental diagnostics in understanding the intricate physical mechanisms in CCPs. In this paper, a 2D particle-in-cell plasma model is used to study the kinetic behavior of low-pressure (<5 Pa) CCPs in two different representative chemistries: Ar and O2. The low-frequency RF source is at 1.356 MHz while 27.12 MHz is used for the high frequency. Simulations show a shift of the peak in the plasma density from the center of the chamber to the edge as the pressure increases from 0.3 to 2.6 Pa. The computed magnitude and spatial profile of electron density compare reasonably with experimental measurements over a range of pressure. Comparison between electro-positive and electro-negative plasmas are discussed. Modeling results for the dual frequency CCP highlight the effect of plasma uniformity on the IAEDF, especially near the outer edge of the electrodes. Collisions in the sheath increase the population of low-energy ions as the pressure is increased to 2.6 Pa.

Investigation of optical spectroscopy in W13+ ions

This study presents the investigation of magnetic dipole transition lines of W13+ ions in the wavelength range of 200–700 nm at a low-energy electron beam ion trap. Seventeen lines emitted from W13+ ions have been observed with three being reported experimentally for the first time. The atomic structure calculation and spectra simulation of W13+ ions have been carried out using the multiconfiguration Dirac–Hartree–Fock method combined with the relativistic configuration interaction approach and the collisional–radiative model, respectively. The theoretical calculations are in reasonable agreement with the experimental observations, and most of the observed lines have been identified.

C-Axis Aligned Composite InZnO via Thermal Atomic Layer Deposition for 3D Nanostructured Semiconductor.

Amorphous oxide semiconductors have been widely studied for various applications, including thin-film transistors (TFTs) for display backplanes and semiconductor memories. However, the inherent instability, limited mobility, and complexity of multicomponent oxide semiconductors for achieving high aspect ratios and conformality of cation distribution remain challenging. Indium-zinc oxide (IZO), known for its high mobility, also faces obstacles in instability resulting from high carrier doping density and low ionization energy. To address these issues and attain a balance between mobility and stability, adopting a highly aligned structure such as a c-axis aligned crystalline IGZO could be advantageous. However, limited studies have reported enhanced electrical performance using crystalline IZO, likely attributed to the high thermal stability of the individual components (In2O3 and ZnO). Here, we first propose a c-axis aligned composite (CAAC) IZO with superior TFT properties, including a remarkable performance of field-effect mobility (μFE) of 55.8 cm2/(V s) and positive-bias-temperature-stress stability of +0.16 V (2 MV/cm, 60 °C, 1 h), as well as a low subthreshold swing of 0.18 V/decade and hysteresis as 0.01 V, which could be obtained through optimization of growth temperature and composition using thermal atomic layer deposition. These results surpass those of TFTs based on nanocrystalline/polycrystalline/amorphous-IZO. We conducted a thorough investigation of CAAC-IZO and revealed that the growth temperature and cation distribution profoundly influence the crystal structure and device properties. Finally, we observed excellent compositional conformality and 97% step coverage of IZO on a high-aspect-ratio (HAR) structure with an aspect ratio reaching 40:1, which is highly promising for future applications. Our results include a detailed investigation of the influence of the crystal structure of IZO on the film and TFT performance and suggest an approach for future applications.

Defect production in tungsten under sub-threshold energy irradiation: role of hydrogen and surface effects

Despite the low solubility of hydrogen isotopes (HIs) in tungsten (W), their concentration can reach up to ∼10 at.% after low-energy plasma irradiation. This is generally attributed to the vacancies that may accommodate excessive HIs. However, the kinetic energy of incident HIs transferred to W is far below the energy threshold to create a Frenkel pair, the underlying mechanism of defect production is still unclear. Here, we investigate the influence of H on the defect production in W using the molecular dynamic (MD) simulations. It is found that the threshold displacement energy (TDE) in bulk W slight decreases with the increasing of H concentration. This is due to the formation of H-vacancy complexes, which prevents the vacancy-interstitial recombination. More importantly, the H effects are significantly magnified in the surface region. On the one hand, the maximum kinetic energy transferred from 400 eV H to W can reach up to ∼21 eV due to the double-hit process, which is two times higher than that predicted by elastic collision model. On the other hand, the momentum transferred to W is completely random, including both the recoil direction upward and downward from the surface. Accordingly, the lowest TDE in W surface is only 15–21 eV at sub-surface layers with the depth of 6.7–11.1 Å, which is lower than the maximum kinetic energy transferred to W. Therefore, the low-energy HIs irradiation can create the defects in W surface directly. Our findings provide deep insight into defect production in W at sub-threshold energy and have wider implications for materials performance under low-energy ions irradiation.

A density functional tight-binding based strategy for modeling ion bombardment and its application to Ar bombardment of silicon nitride

In many modern applications, it is important to understand mechanisms of non-equilibrium chemistry and physics that are driven by low energy ion bombardment of solid surfaces. However, the study of these processes has been challenging as it demands a relatively unique balance between chemical fidelity and computational cost. To this end, we have proposed and constructed a new, high-throughput simulation pipeline based on density functional tight binding simulations. Additionally, we have extended the parameter set pbc-0-3 with the addition of Ar, thereby enabling the simulation of Ar bombardment. This pipeline was then applied to study the structural and compositional evolution of silicon nitride (SiN) under Ar bombardment. We identified a possible rate limiting step of bombardment-driven sputtering of SiN and suggested underlying mechanisms of Si and N removal. Damage from the bombardment, including generation of surface defects and Ar implantation, are further discussed. These findings and the newly developed simulation framework will serve as a useful foundation for further research in processes driven by ion bombardment.

Antibacterial Surfaces Treated with Metal Ions Incorporation by Low-Energy Ionic Ion Implantation: An Opinion

Infectious diseases have been a huge obstacle to human survival for centuries. Despite scientific progress, bacterial infections continue to be among the leading causes of death and disability worldwide. Thus, surface functionalization of materials can be a viable strategy to prevent biofilm formation. In this way, metal ions incorporation, such as silver (Ag+), copper (Cu2+), or zinc (Zn2+), have been proposed due to their antimicrobial properties, and low-energy ionic ion implantation (IPD) as promising alternative surface treatment process. Therefore, this article briefly reports on recent developments in this technique in surface functionalization for antibacterial action. Furthermore, it seeks to point out perspectives for applying the technique and points for improvement for this technology.

Crystallinity as a factor of SERS stability of silver nanoparticles formed by Ar+ irradiation

The plasmonic sensors based on silver nanoparticles are limited in application due to their relatively fast degradation in the ambient atmosphere. The technology of ion-beam modification for the creation of monocrystalline silver nanoparticles (NPs) with stable plasmonic properties will expand the application of silver nanostructures. In the present study, highly-stable monocrystalline NPs were formed on the basis of a thin silver film by low-energy ion irradiation. Combined with lithography, this technique allows the creation of nanoparticle ensembles in variant forms. The characterization of the nanoparticles formed by ion-beam modification showed long-term outstanding for Ag nanoparticles stability of their plasmonic properties due to their monocrystalline structure. According to optical spectroscopy data, the reliable plasmonic properties in the ambient atmosphere are preserved for up to 39 days. The mapping of crystal violet dye via surface-enhanced Raman spectroscopy (SERS) revealed a strong amplification factor sustaining at least thrice as long as the one of similarly sized polycrystalline silver NPs formed by annealing. The plasmonic properties sustain more than a month of storage in the ambient atmosphere. Thus, ion-beam modification of silver film makes it possible to fabricate NPs with stable plasmonic properties and form clusters of NPs for sensor technology and SERS applications.

Low-energy ion beam diagnostics: an integrated solution

High gradient accelerator injectors have been widely studied throughout the world-leading accelerator facilities. The demand for high frequency cavities has led the Detector, Accelerator and instrumentation laboratory (KAHVELab) in Istanbul to deploy a four-vane Radio Frequency Quadrupole (RFQ) operating at 800 MHz to accelerate 20 keV protons to 2 MeV. The protons from the microwave discharge ion source are transversely matched to the RFQ via an optimized Low Energy Beam Transport (LEBT) line which also contains an integrated measurement station, called measurement station (MBOX). The MBOX is used to measure the proton beam's current along with pulse length duration, profile as well as the beam emittance upstream of the RFQ. It contains a number of home-built diagnostic tools: a Faraday cup, a scintillator screen and a pepper pot plate (PP). The analysis software is also locally developed and tested for the PP photo analysis. In this note, the design, construction and tests of the integrated measurement station are discussed. The results from various measurements, especially on beam profile and charge, are compared to the simulation predictions.

Cone array formation on Si surfaces by low-energy He plasma irradiation with magnetron sputtering pre-deposited Ta

Low-energy ion beam irradiation, combined with the introduction of impurities, presents a promising approach for nanopatterning silicon (Si) surfaces. In this research, we investigate the surface evolution of Si (100) surfaces irradiated by 75 eV helium (He) plasma, in the presence of tantalum (Ta), traditionally regarded as an impurity incapable of initiating pattern formation, as evidenced in prior studies. The Ta impurities are pre-deposited onto the Si surfaces using the magnetron sputtering method, which offers a more controlled and quantifiable approach compared with the conventional co-deposition route. After irradiation at 800 K, dense cone arrays are produced on the Si surface. The growth of the cones is explored for fluence spanning (1–10) × 1025 m−2. The cross-sectional scanning electron microscope images indicate that the cone lengths and base width are well characterized by t1/2 dependence. The kinetics of the cone growth follow Fick’s law, characterized by an effective diffusive mechanism with the coefficients of diffusion: D = 6.49 ± 0.83 × 10−16 m−2 s−1. Transmission electron microscope observations reveal that the cone has distinct inner and outer parts with different microstructures and a clear interface. The growth mechanism of these cones is elucidated as a composite process involving preferential sputtering, the destabilizing influence of He bubbles, and the migration of adatoms.

First-principles prediction of n-type diamond: novel co-doped structure using N and Be impurities

To address the limitation of diamond-based electronic devices, a comprehensive study on n-type diamond is crucial. A novel dopant structure, nitrogen–beryllium co-doping, is proposed for achieving n-type doping. The dopant structure, electronic property, synthesis route and internal strain are analyzed using first-principles density functional theory. The formation energy and ionization energy of xN–Be (x = 1–4) are compared to elucidate the distinct doping effects associated with varying numbers of N atoms. The formation energy initially decreases and then gradually increases with an incensing number of N atoms. Notably, 3N–Be and 4N–Be exhibit appealing n-type diamond properties, with low ionization energies of 0.30–0.41 eV (3N–Be) and 0.23–0.37 eV (4N–Be). To facilitate the preparation of 3/4N–Be co-doped diamond, a non-molecular synthetic route is proposed, involving the prior generation of the 3N-V and 4N-V. The 3/4N–Be co-doped diamond exhibits relatively small strain energy. Finally, this investigation highlights the potential of 3/4N–Be co-doping as excellent choices for n-type dopants, providing a greater variety of n-type structures with similar ionization energy compared to 4N–Li co-doping.